Use wtap_read_bytes() to skip over bytes when reading a record.

Allow file_read() to take a null pointer as a buffer argument; a null
argument means "do everything except copy the bytes from the file to the
user buffer".  That means that wtap_read_bytes() and
wtap_read_bytes_or_eof() also support a null pointer as a buffer
argument.

Use wtap_read_bytes() with a null buffer argument rather than
file_skip() to skip forward over data.

This fixes some places where files were mis-identified as ERF files, as
the ERF open heuristics now get a short "read" error if they try to skip
over more bytes than exist in the file.

Change-Id: I4f73499d877c1f582e2bcf9b045034880cb09622
Reviewed-on: https://code.wireshark.org/review/17974
Reviewed-by: Guy Harris <guy@alum.mit.edu>

1 files changed, 10 insertions, 9 deletions

diff --git a/wiretap/capsa.c b/wiretap/capsa.c
index 6f6ea15d30..1d65c1c33b 100644
--- a/wiretap/capsa.c
+++ b/wiretap/capsa.c
@@ -173,7 +173,7 @@ wtap_open_return_val capsa_open(wtap *wth, int *err, gchar **err_info)
 	/*
 	 * Link speed, in megabytes/second?
 	 */
-	if (!file_skip(wth->fh, 2, err))
+	if (!wtap_read_bytes(wth->fh, NULL, 2, err, err_info))
 		return WTAP_OPEN_ERROR;
 
 	/*
@@ -181,19 +181,19 @@ wtap_open_return_val capsa_open(wtap *wth, int *err, gchar **err_info)
 	 * and two of which are zero?  Two 2-byte numbers or flag fields,
 	 * both of which are 1?
 	 */
-	if (!file_skip(wth->fh, 4, err))
+	if (!wtap_read_bytes(wth->fh, NULL, 4, err, err_info))
 		return WTAP_OPEN_ERROR;
 
 	/*
 	 * File size, in bytes.
 	 */
-	if (!file_skip(wth->fh, 4, err))
+	if (!wtap_read_bytes(wth->fh, NULL, 4, err, err_info))
 		return WTAP_OPEN_ERROR;
 
 	/*
 	 * Zeroes?  Or upper 4 bytes of file size?
 	 */
-	if (!file_skip(wth->fh, 4, err))
+	if (!wtap_read_bytes(wth->fh, NULL, 4, err, err_info))
 		return WTAP_OPEN_ERROR;
 
 	/*
@@ -251,7 +251,7 @@ static gboolean capsa_read(wtap *wth, int *err, gchar **err_info,
 		 * first byte.
 		 */
 		capsa->base_offset = file_tell(wth->fh);
-		if (!file_skip(wth->fh, 1, err))
+		if (!wtap_read_bytes(wth->fh, NULL, 1, err, err_info))
 			return FALSE;
 
 		/*
@@ -265,7 +265,7 @@ static gboolean capsa_read(wtap *wth, int *err, gchar **err_info,
 		 * And finish processing all 805 bytes by skipping
 		 * the last 4 bytes.
 		 */
-		if (!file_skip(wth->fh, 4, err))
+		if (!wtap_read_bytes(wth->fh, NULL, 4, err, err_info))
 			return FALSE;
 	}
 
@@ -283,7 +283,7 @@ static gboolean capsa_read(wtap *wth, int *err, gchar **err_info,
 	 * Skip over the padding, if any.
 	 */
 	if (padbytes != 0) {
-		if (!file_skip(wth->fh, padbytes, err))
+		if (!wtap_read_bytes(wth->fh, NULL, padbytes, err, err_info))
 			return FALSE;
 	}
 
@@ -339,8 +339,9 @@ capsa_read_packet(wtap *wth, FILE_T fh, struct wtap_pkthdr *phdr,
 		 * XXX - what is that?  Measured statistics?
 		 * Calculated statistics?
 		 */
-		if (!file_skip(fh, (capsarec_hdr.count1 + capsarec_hdr.count2)*4,
-		    err))
+		if (!wtap_read_bytes(fh, NULL,
+		    (capsarec_hdr.count1 + capsarec_hdr.count2)*4,
+		    err, err_info))
 			return -1;
 		header_size += (capsarec_hdr.count1 + capsarec_hdr.count2)*4;
 		break;